Regional monitoring of lead and cadmium contamination in a tropical grazing land site, Thailand.

Abstract

An investigation was carried out to monitor Pb and Cd contamination in grazing land located near a highway. Environmental media at different distances from highway (soil, grass, water, cow's forage, fertilizer, manure and milk samples) were collected from three sampling locations. Soil and grass were characterized by high metal mobility (soil with Pb: 5.25 +/- 0.71-14.59 +/- 1.17 mg kg(-1), dry mass and Cd: 0.038-0.33 +/- 0.04 mg kg(-1), dry mass and grass with Pb: 0.76 +/- 0.05-6.62 +/- 0.18 mg kg(-1), dry mass and Cd: 0.17+/- 0.01-0.73 +/- 0.09 mg kg(-1), dry mass). One-way analysis of variane (ANOVA) was applied to find out the correlation between metal (total and bioavailable) concentrations in the soil and the distance from roadside. In most cases, the finding showed that plants growing nearer to the highway are usually exposed to more heavy metal accumulations than those away from the highway. In addition, a correlation was established between plant available metal concentrations and plant metal uptake concentrations. Analysis of fertilizer and manure showed considerable amount of metals (fertilizer with Pb: 1.53 +/- 0.06 mg kg(-1) and Cd: 0.038 mg kg(-1) and manure with Pb: 2.55-3.34 mg kg(-1) and Cd: 0.14-0.31 mg kg(-1)). Long-.term simultaneous application of fertilizer and manure on the commercial farm showed higher metal accumulation in the soil and plants than those of co-operative farm. Considerable concentrations of metals (Pb: 1.60-2.94 mg kg(-1) and Cd: 0.025-0.19 mg kg(-1)) were observed in fodder. The finding clearly demonstrated that there are seasonal variation in total daily metal intake by individual cow (Pb: 109.37 mg day(-1) (dry), 273.47 mg day(-1) (rainy) and Cd: 2.02 mg day(-1) (dry), 19.62 mg day(-1) (rainy)). The provisional tolerable weekly intake of heavy metals in cows is 390 microg Pb and 28 microg Cd per kg body weight in the rainy season and 156 microg Pb and 2 microg Cd per kg body weight in the dry season. The levels of metals (Pb: 0.014 mg L(-1) and Cd: not detectable) and bio-transfer factor (10(-5)-10(-4)) in raw milk were found to be well below the Codex Alimentarius Commissions Draft (1997). Our analysis revealed that improvements on farm management give significant reduction in elevated levels of Pb and Cd in soil and plants, and however leads to minimize the amount of Pb and Cd in consumed milk.